Quartz-to-metal seal



(fig x r April 1950 A. GREHNER 2,

QUARTZ-TO-METAL SEAL Filed ma 1, 1948 T ig. 4.

2/ [Z 20 g r 1 z d Inventor': ALFFfiECl Gveiner,

Patented Apr. 18, 1950 UNITED ST PATENT? ouAnrz-r iji rhn AlfredGreiner; Cleveland Heights,.0hio,' assignor tolGeneral Electric Company,a corporation of N ew York Application May 1, 1948, Serial No. 24,523

12'Claims.

My invention relates to'quartz-to-metal seals for high pressuredischarge devices, such as high pressure mercury vapor discharge lamps.

Lamps of this 'kind are high intensity light sources and'may-operatewith-a power-consumption in the order of several kilowatts and-a vaporpressure of many atmospheres; One type of such lamp'comprises aspherical quartz envelope having seals in the form of protruding stemssupporting theelectrodes and including leading iii-conductors in theform of multiple-molybdenum' foils connected in parallel to carry theheavy discharge current and fusedinto the quartz body of-the stem. Thefoils are extremely thin andtherefore require careful and skilledhandling in making the stem.

An object of my invention is .toprovide a quartzto-metal seal in theform of"a stem which is of simple structure. Another object of myinvention'is to provide-a method: of making such a stem. A furtherobject of my invention" is to provide a method of making aquartzto-metal seal. Other objects and advantages of the in vention'willappear from the following description of species thereof-taken inconjunction with the accompanying drawing in which Fig. 1 is anelevational view, partly in section, of a lamp having stems embodying myinvention; Fig. 2 is an exploded view ofthe metal parts of the stemshown in'section in Fig. 1; Fig. 3'is a sectional elevational View ofvitreous tube constituting part of the stem; Fig. 4-is a similar view ofanother quartz tube also constituting part of the stem; and Fig; 5 isasimilar view of the stemelements of Figs. 2 to 4 assembled for fusiontogether.

Theda-mp shown' in Fig. 1 of'the drawing is of the high vapor pressureelectric discharge type having a. spherical quartz envelope I providedwith quartz-'to-metal seals in "the form of alignedstems 2 and3'protruding. from diametrically opposed portions thereof. Thestems-Zand 3-are identical in structure-and have lead-in conductors includingtungsten" rods 4 and 5 extendingthrough quartz stem tubes and carryingelectrodes G and l at their inner ends. Rods 4 and 5 are exposed attheir outer ends for connection to the terminals of a power source forthe lamp.

The electrodes 6' and l are closely spaced in the center of the quartzenvelope I Which'com tains an ionizablegaseous atmosphere includ-- ing-astartinggas, sucl1'asarg0n', and mercury in an amount sufficient toproduce-on the power? input for which the-'lanipis-designedanun-*saturated vapor atmosphere" having a: pressure 2. of the order ofatmospheres; A vapor pressure of.- the order of 300 pounds per squareinch-or mat mospheres'maybe produced in'such a lamp hav ing a-powerconsumption-of about 10 kilowatts.--

In order to carry such large currents-,the-tungr sten rods 4 and 5 mustbe of such large diameter. that quartz cannot be fuseddirectly'thereto-ytw make a fused joint-which will-be'gasP-tight'underrthe conditions of-operation.

To provide such a joint I utilize thimblesd -of refractory metal, suchasmolybdenum or tung sten, positioned in the stemrtubesand around thesrods4 and 5. The thimbles fl are hermetically=- united with the rods; ,4 and5: andha-ve-afeather ed'sealing edge 8; The quartz of the. stems-.zand 3is fused to both the: inner and-outer: surfaces of the edge- 9, asdescribed below, to make amechanically strong and ,temperature-reslstantf quartz-to-meta'lseal. The quartz parts: of -the stems surroundingthe thimblesand the-rods;provide good support therefor tohold theelectrode'si 6 and l in proper position inthe'envelope-l As best-shownin Figs. 2' and"5. the outer sur face of the'thimble' 8 back from theportion-.to" which the quartzis fusedand theportion.of tlzle -v rod 4extending'from'the thimble 8'to.ward th e electrode 6 are sheathed withmolybdenum'foilii! which acts as a cushion between-the quartz tube andthe parts of the rod and the thlmble covered by the foil. Thisfoil.covering; thethicla ness of which is greatly'exaggerated in the, draw;-ing, prevents the quartz-from adhering-to thesethick-metal partsduring-fabrication of thestem. and avoids cracking of the' quartz when'these metal parts-expand and contract in respons'ertochanges intemperature.

A metal spacer H inside the thimblea serves-r the-same purpose bypreventing the qua-rtz .;from. going -so far into the thimbleduringfabrication:

that it would fuse-not only to the inner surface of the featheredsealing edge 9 of the thimblec-w but also toother thicker portionsofthevinner surface of the. thimb'lei' Thusy'the' only portiontoftheconductor, cluding the rod 4 and the metai thimblegat to whichthe'uuartzds"hermeticalfy fusd'is'the' afl nular; tapered;feathered-sealing.- edge 9: whiclrs is-of'suchthin wall section thatthe-quartz; ad heres to-b'oth the" innerandouter surfaces-thaw ofwithout cracking duringfabricatiomandwusev ofthe' stem. v

In making the stem; the thimble 8 is; cut-and. ground" to shape: from:bar-or flat-molybdeninrr stock; As best showrrin-Fig; 2 of thedrawing-git has-adomed=shaped closed end having an opening I2 for therod 4. A specific embodiment of a thimble which has given good resultshas its annular side .wall '7 of an inch in depth with an inner diameterof of an inch and tapers from the closed end to the feathered sealingedge 9 which is between 0.0006 to 0.001 of an inch in thickness at itsend. About inch back from the end of the edge 9 the wall thickness isbetween .0016 and .002 of an inch. I have demonstrated that these upperlimits are critical; the quartz will break away from the metal surfaceor crack and the seal will leak if the upper limit is exceeded.

The flanged spacer II inside the thimble 8 is also made of molybdenum.It is of an inch long, the cylindrical part thereof is of an inch inoutside diameter and the flange part I3 slightly less than of an inch indiameter so that there is small clearance between it and the innersurface of the annular thimble wall. The tungsten .5.

rod 4 passing through the opening I2 in the thimble 8 and through thespacer II is approxi mately $4 of an inch in diameter and the openingsin the spacer II and in thimble 8 are made just large enough toaccommodate the rod 4. The spacer I I holds the rod and the thimble inalignment during the brazing operation by which these three members arejoined together after they are assembled as shown in Figs. 1 and 5.

I prefer to use platinum as the brazing material to bond the three metalmembers together. This metal withstands the high temperatures existingthereat during fabrication and use of the stem and forms a hermeticjoint between the tungsten rod 4 and the molybdenum thimble 8.

After the rod 4, the thimble 8, and the spacer I I have been joinedtogether they are thoroughly cleaned and the metal sheath I is applied.The sheath consists of two sheets of molybdenum foil approximately .0006of an inch thick wrapped around the parts of the rod 4 and the thimble 8to be covered. One of the sheets is shaped in the form of a collar I0wrapped around the domed end of the thimble 8, the part of the rodemerging from the closed end of the thimble and the part of the annularwall of the thimble adjacent the domed bottom. The foil collar I0 coversthe brazed joint between the rod and the thimble and extends to withinof an inch of the feathered edge 9 of the thimble 8. The collar I0 ispreferably shaped from a foil strip approximately of an inch wide and 2%inches long. One long edge of the strip is serrated to a depth ofapproximately of an inch with a distance of an inch between serrationswhich overlap when the strip is wrapped around the thimble and the rodto form the collar. The tab is welded to the surface of the strip afterthe collar is formed. In Fig. 2 the collar is shown removed from thethimble for purposes of illustration.

The foil sheet In wrapped around the rod 4 may overlap the end of thecollar slightly and is made of a sheet approximately 1%; inches wide and1% inches long.

This assembly of the metal members is insorted in the two quartz tubesI4 and I5 shown separately in Figs. 3 and 4, respectively. The completeassembly before fusing the various elements of the stem together isshown in Fig. 5.

The quartz tube I4 surrounding the thimble 8 and the outer end of therod 4 is made up of three overlapping coaxial tubes l6, l1, and I8, thetube I8 of smallest diameter being of an inch in outside diameter, 6inches long and 1 g of an inch thick, the tube of largest diameter I8being of an inch in outer diameter, of an inch in inner diameter and 2inches long, and the intermediate tube I! being slightly larger than ofan inch in outer diameter and of an inch thick. The ends of the tubesI6, ,II, and I8 are fused together as shown in Fig. 3. The tubes I1 andI8 form a longitudinally extending annular recess opening into theinterior of the tube I4 and which accommodates the feathered edge 9 ofthe thimble 8 with the said edge 9 touching or in close proximity to thefused joint between the tubes I1 and I8 and the flange I3 on the spacerII resting against the fused joint between the tubes I6 and I! as shownin Fig. 5.

The quartz tube I5 surrounding the inner end of the rod 4 has a thickwall portion I9 approximately 3% inches long which surrounds the rod 4in the completed stem and a thinner wall portion 20 approximately 5inches long. The thicker wall portion I9 has an outer diameter of of aninch, an inner diameter slightly greater than inch to accommodate therod 4 and the sheath ID, a flare 2| about 11% of an inch in diameter atthe end thereof to be inserted in the end tube I8 of the quartz tube I4and a bulge or bulbous portion 22 of about %3- of an inch outsidediameter at the end joining the thin wall portion 20 thereof.

In the assembly including all the elements shown in Fig. 5 the portionI8 of the tube I4 overlaps the end of portion I9 of tube I5 with theflare 2| on the latter making a close mechanical fit with the innersurface of the tube portion I8. The two quartz tubes I4 and I5 then forma chamber for the metal parts. In completing the stem a non-oxidizinggas, such as nitrogen or forming gas which is a mixture of hydrogen andnitrogen, is first caused to flow into the chamber through the open endof each of the tubes I4 and I5. This gas fills the chamber to preventoxidation of the metal parts therein during heating of the quartz parts.It flows out of the chamber between flare 2| and tube portion I8. Theflare 2| prevents too rapid escape of the gas from the chamber formed bythe tubes I4 and I5 before these are fused together.

With the gas flowing as described above, heating flames are applied tothe tube portion I8 surrounding flare 2I and overlapping the tube por--tion I9. During this heating step and before the overlap of tube I8collapses onto the flare 2| to seal the opening between them, the streamof gas passing between the flare 2| and the inner surface of tubeportion I8 prevents products of combustion from the heating flameentering the chamber and affecting the metal parts. When the heatedquartz becomes plastic and closes the space between the flare 2| and thetube portion I8, the pressure of the gas in the chamber is immediatelyreduced to only slightly above atmospheric pressure to avoid blowing outthe plastic quartz as the overlapping portions of the tubes I4 and I5are being fused together.

After the tubes I4 and I5 have been spliced together in the above mannerthe assembly is allowed to cool to room temperature with the gas stillflowing through the chamber. The chamber is then exhausted to a highvacuum and, while the vacuum is maintained, the metal parts are heatedby a high frequency oscillator to remove any gas which may have formedon these parts during the splicing of the tubes I4 and I5. The assemblyis again allowed to cool until it may be sealed off from the vacuumsysest th he sinister n. a hi hl ei st andide-e. As sh wn d tted lines and Q 1 l 5, oth ends. of the chamber formed y he. uarts tubes .4 and ara e aheetins were s then p ied a h Juneure o l 8 surr und-iris thefeathered sealing edge 9 of the thirnble 8 to soften and lla sethe e tbes simu ee cusly n ot des f-t e ed e 9- f h himb and to m k a u edbermetie Jointv t en th u r a d th hiiab e, Peri-as h s h a i tep w s bexerci ed- 9 hea both f theSC u s H n "i at heser at o t their reasin no.tions collapse simultaneously back from their juncture and. contact withthe inner and uter-- surfases c t i athe c sc l n e If wells collapse atdifferent rates, the thin wall ofthe thimble will either be split if thenner tube l eclla scs nt e a e therefist, or will wrinkle if the outertube i8 doessoii t.

The oil sheath on the outside of the thimble 8 the flange I33 0n thespacer H prevent the tubes If! and H; from fusing with the thickerportion o he t in l llbetween the quartz and the thimble edge 9 isapprogzi nately of inch long on the outside and about ofan inch long onthe inside of the thimble wall measured back from the end edge a so thatthe seal has an overall length o aoproi ma e y e nch s and i of largeea- ;t-he hermetic seal has been formed the quartz tubing surroundingthe foil covered portion of the thimble and the tungsten rod is heated,starting from the thi nble, to collapse the quantz onto the sheath 10 togive good mechanical support to the metal par-ts of the stern. Due tothe sheath 10 the quartz does not adhere to the rod 4 or the coveredportion of the thimble. The assembly is again allowed to cool and thesurplus quartz tubing is severed and removed at about the maximumdiameter of the bulge 22 and at a point approximately inch from theopposite end of the rod 4 to complete the stem. One end of the rod 4 isthus exposed for connection to a power source when mounted in a lamp andthe other end, which is the inner or electrode end of the rod, extendsan appreciable distance beyond .the remaining part of the bulge and intothe lamp envelope when the remaining bulge part, which constitutes asealing flange for fusion with the quartz envelope of the lamp, isjoined to the lamp envelope as shown in Fig. l.

The cathode 5 of the high pressure lamp is constituted by the inner endof rod 4 which is shaped in the form of a wedge and preferablyimpregnated with material having high elec tron emissivitycharacteristics, such as thorium. The anode l is constituted by a blockof tungsten welded to the end of rod 5. In making the lamp, electrodes 5and l are inserted into the quartz envelope 1 through diametricallyopposed openings and the flanges on the stems are fused into saidopenings to close them and to support the electrodes in proper spacedapart positions in lamp. The lamp is completed by steps well known inthe art, including evacuation and introduction of the gas filling andmercury.

In the co-pending application of Leo R. Peters, Serial No. 24,522, ofeven filing date herewith and assigned to the assignee of the present.application, themethod of brazing the tungsten and molybdenum parts ofthe conductor together and the article produced by the method aredisclosed and claimed.

The hermetic seal d I la m as w and d si e o tee s 3 Letters ten r e wassates s Th meth d o maki a stem f e m ws el which ompr s um n f a es bew th a l d n ll 'e isn i a l l's e? s op nin n its inte qr ins a mate! oductor n lud ng a we a d a himb can a od and h me all un ther w t anthirnble having a feathered sealing egg?- covering th or on of a d rednd wa d from the closed end of the thimble and said thirnble, other thanthe feathered sealing edge ofthe latter, with a metal foil, positioningsaid conductor in said tube with the feathered seal: ing edge in saidrecess, positioning a second vitreous tube around the foil-coveredportion of, the, rod and fusing it to said first-named tube to form acomposite tube, reducing the pressure in said composite tube belowatmospheric, heating the wall of the recess on both sides ofsaid edge o.c llapse. s id wall n b t of i s e multaneously to fuse said wall tosaid edge without deforming. the latter and then heating the portion ofthe composite tube surrounding the foil covered portion of said thimbleand said 110. 1 collapse said portion onto said metal foil so that saidcomposite tube tightly fits said thimble and said rod and providesmechanical support for said conductor in said composite tube.

2,. The method ofmaking a mechanically strong. electrically conductinggas-tight seal for i h capacity. high pressure dischar e. quartz lampswhich comprises hermetically joining a molybdenum thimble having afeathered sealing edge around a tungsten rod passing through thethimble, forming a quartz tube with a longitudinally extending annularrecess opening into its interior, positioning the thimble in said tubewith its feathered edge in said recess and the rod .ex-

tending along the tube and exposed beyond one end thereof, positioning asecond quartz tube around the exposed .end of the rod and telescopedwithin said first-named tube, filling said tubes with a non-oxidizingatmosphere. fusing the telescoped .tube portions together to form achamber.

evacuating the said chamber, heating the wall of the recess on bothsides .of the feathered edge of the thimble to collapse said wall ontoboth of said sides simultaneously to fuse said wall to said edge withoutdeforming the latter and then heating the wall of said chambersurrounding the remainder of said thimble and said rod to collapse saidwall so that it tightly fits said thimble and said .rod to providemechanical support therefor.

3. A high-pressure-resistant stem tor electric devices comprising anelongated vitreous stem tube, a lead-in conductor extending along saidtube and beyond each of its ends and a thimble wholly within said tubeand hermetically joined to and disposed around said conductor'wlth itsclosed end'toward the inner end of the conductor. said thirnble having afeathered sealing edge embedded =in and making a-fused joint with thewall of the stem tube said tube tightly fitting the .exterior of saidthimble and at least the portion of said conductor extending outwardfrom' the closed end of the thimble'to provide mechanical supporttherefor.

1. A high-pressureresistant stem for electric devices comprising anelongated vitreous stem tube. a lead-in conductor extending along saidtube and beyond each of itsend's'and a thimbl'e wholly within said tubeand hermetically joined (6 to and disposed around said conductor withits closed end toward the inner end of the conductor and with the endsof the conductor extending beyond the thimble ends, said thimble havinga feathered sealing edge embedded in and making a fused joint with thewall of the stem tube, said tube tightly fitting the portions of saidconductor extending from said thimble and said thimble to providemechanical support therefor.

5. A high-pressure-resistant stem for electric devices comprising avitreous stem tube, a leadin conductor extending along said tube and athimble wholly within said tube and hermetically joined to and disposedaround said conductor with its closed end toward the inner end of theconductor, aid'thimble having a feathered sealing edge embedded in andmaking a fused joint with the wall of the stem tube, said stem tube wallextending into said thimble, and a cylindrical member around saidconductor and butting against the tube wall in said thimble and theclosed end of the thimble to reinforce the latter.

6. Ahigh-pressure-resistant stem for electric devices comprising avitreous stem tube, a leadwall closely surrounding said conductor andsaid thimble to provide mechanical support therefor,

and a loose metalfoil covering portions of said conductor and saidthimble to prevent said tube adhering to said portions.

-7. A high-pressure-resistant stem of high capacity for electricdischarge quartz devices comprising an elongated quartz stem tube, atungsten rod extending along said tube and beyond its ends and amolybdenum thimble wholly within said tube and hermetically joined toand disposed around said rod with its closed end toward the inner end ofthe rod, said thimble having a feathered sealing edge embedded in andmaking a fused joint with the wall of the stem tube said tube tightlyfitting the exterior of said thimble and at least the portion of saidrod extending fro'mt-he closed end of the thimble to provide mechanicalsupport therefor.

8. A high-pressure-resistant stem of high capacity for electricdischarge quartz devices comprising an elongated quartz stem tube, atungsten rod extending along said tube and beyond its ends and amolybdenum thimble wholly within said tube and hermetically joined toand disposed around said rod with its closed end toward the inner end ofthe rod, said thimble having a feathered sealing edge embedded in andmaking a fused joint with the wall of the stem tube, and a molybdenumfoil sheath extending'from the fused joint and covering th exterior ofsaid thimble and the portion of said rod extending inward of the stemtube from the closed end of the thimble, said stem tube tightly fittingthe sheathed portions of said thimble and said rod to provide mechanicalsupp rt therefor.

9. In a high pressure resistant stem for electric devices, a conductorrod, 2. metal thimble around said rod and a cylindrical metal spaceralso around said rod and butting against the inner surface of thethimble, said rod and said thimble being rigidly bonded together with agastight joint therebetween.

10. In a high pressure resistant stem for electrio devices, a. tungstenrod, a molybdenum thimble around said rod and a molybdenum spacer alsoaround said rod and butting against the inner surface of the thimble,said rod and said thimble being rigidly bonded together with a gas-tightjoint therebet'weeri.

11. A high-pressure-resistant stem of high capacity for electricdischarge quartz devices comprising an elongated quartz stem tube havinga flared end for fusion with the envelope of said device, a tungsten rodextending along said tube and beyond each of its ends and a molybdenumthimble wholly within said tube and 'hermetically joined to and disposedaround said rod with its closed end toward the flared end of the stemtube and with the ends of the rod extending beyond the ends of thethimble, said thimble having a feathered sealing edge embedded in andmaking a fused hermetic joint with the wall of the stem tube, amolybdenum foil collar around said thimble and extending from the fusedjoint to the said rod and a molybdenum foil sheatharound said rod andextending from said thimble to adjacent the flared end of said stemtube, said stem tube tightly fitting the sheathed portion of saidthimble and both ends of said rod to provide mechanical support for saidrod and said thimble in said stem tube.

12. A high-pressure-resistant stem of high capacity for electricdischarge quartz devices com prising an elongated quartz stem tubehaving a flared end for fusion with the envelope of said device, atungsten rod extending along said tube and beyond each of its ends and amolybdenum thimble wholly within said tube and hermetically joined toand disposed around said rod with its closed end toward the flared endof the stem tube and with the ends of the rod extending beyond the endsof the thimble, a molybdenum spacer' around said rod and in said thimbleand butting against said rod and said thimble, said thimble having afeathered sealing edge embedded in and making a fused hermetic jointwith the wall of the stem tube, a molybdenum foil collar around saidthimble and extending from the fused joint to the said rod and amolybdenum foil sheath around said rod and extending from said thimbleto adjacent the flared end of said stem tube, said stem tube tightlyfitting the sheathed portion of said thimble and both ends of said rodto provide mechanical support for said rod and said thimble in said stemtube.

ALFRED GREINER.

REFERENCES CITED The following references are of record in the file ofthis patent:

